Plant S1 SINEs as a model to study retroposition

The S1 element is a plant SINE (Short INterspersed Element) that was first described and studied in Brassica napus and is widely distributed among Cruciferae, especially in species of the Brassiceae tribe. We propose that S1 amplification in Cruciferae could represent a good eukaryotic model to study retroposition. This is based on the fact that S1 elements share clear structural and evolutionary characteristics with mammalian SINEs but are present in a much lower copy number (500 loci by haploid genome for the S1 element in B. napus compared to 700,000 loci by haploid genome for the Alu element in human). This low copy number allows the characterization of a large portion of SINEs from a given plant species. This can lead to a more precise understanding of the evolutionary history of SINE amplification and can more easily allow an evaluation of the impact of retroposition on the evolution of that species. It can also lead more rapidly to the characterization of genomic elements active in transcription and retroposition so that the cellular control of these elements can be addressed. Finally, we show that the study of S1 insertion sites can reveal information on the RNA reverse transcription and integration step of the retroposition process.